ABSTRACT
The adrenal glands are retroperitoneal structures, sitting on the anteriomedial aspect of the upper pole of each kidney. They are composed of the cortex, of mesodermal origin, which consists of three layers (zona glomerulosa, zona fasciculata and zona reticularis), and the medulla, of neuroectodermal origin, which is enveloped by the cortex. The fetal adrenal gland is enlarged because of a markedly thickened cortical layer, the fetal cortex, which is covered by a thin layer of what will eventually become the cortex in the adult. Soon after birth the fetal cortex begins to involute. Mineralocorticoids (including aldosterone) are being secreted by cells of the zona glomerulosa. Cells in the zona fasciculata and reticularis secrete glucocorticoids and sex hormones, whereas adrenalin and noradrenalin are being produced by the cells of the medulla under the influence of sympathetic preganglionic fibers. Because of their size the neonatal adrenal glands are very easily visualized by ultrasound (US). On longitudinal scans they appear as V or Y shaped structures composed of a hyperechoic inner layer, repre senting the medulla, and a hypoechoic outer cortex (Figure 1). On transverse scans the glands have an elongated elliptical shape, with a more or less linear inner hyperechoic layer (medulla) surrounded by the hypoechoic cortex (Figure 2).
